How to return to the default view that you see when blender starts?
If you want to reset the default viewport view and not the camera view,run this in text editor :

import bpy


vm = ((0.41, -0.4017, 0.8188, 0.0),(0.912, 0.1936, -0.3617, 0.0),(-0.0133, 0.8959, 0.4458, 0.0),(0.0, 0.0, -14.9892, 1.0))

for area in bpy.context.screen.areas:
    if area.type == 'VIEW_3D':
        v3d = area.spaces[0].region_3d
        if v3d :
            v3d.view_matrix = vm
            v3d.view_perspective = 'PERSP'


if you are wondering where those values are from , i simply started the default scene and used
print(v3d.view_matrix) to get the default coordinates.